A century-old tuberculosis vaccine appears to offer protection against COVID-19, according to back-to-back peer-reviewed studies by international scientists.

The researchers from India, China, US and Italy reported^[1]Sharma, A., Kumar Sharma, S., Shi, Y. et al. BCG vaccination policy and preventive chloroquine usage: do they have an impact on COVID-19 pandemic?. Cell Death Dis 11, 516 (2020). https://doi.org/10.1038/s41419-020-2720-9 in the Nature journal Cell Death & Disease that Countries with a universal Bacillus Calmette-Guerin (BCG) vaccination policy show the lowest COVID-19 but the BCG strain used in the vaccine also has a major bearing.

The team led by Dr. Abhibhav Sharma from School of Computer and System Sciences, Jawaharlal Nehru University, New Delhi, India, reported that “that countries without a universal BCG policy (such as Belgium, Italy, the United States, and the Netherlands) have increased incidence of COVID-19 compared with countries with ongoing national BCG policy.”

“The incidence for countries that discontinued BCG vaccination was intermediate between these two groups,” the scientists stated. 

“In terms of morbidity, the countries with a universal BCG policy exhibited the lowest number of deaths due to COVID-19, which is significantly lower than that for countries that discontinued universal BCG vaccination. Countries with no BCG vaccination were most profoundly affected,” the researchers added.

But not all BCG vaccines are created equal, the researchers warned.

“We found that countries adopting a mixture of different strains of the BCG vaccine such as South Korea and the Philippines reported a lower number of confirmed and fatal cases,” the researchers reported. “The BCG-Denmark and BCG-Russia strains correlated poorly in terms of limiting the COVID-19 spread and casualty.”

This may explain why incidence and morbidity rates are high in Brazil, a country with a universal BCG vaccination policy.

“Even if it is a country with universal BCG vaccination policy, the number of deaths due to COVID-19 is the highest among the countries with similar vaccination strategy,” the scientists explained. “This could be due to the use of the BCG-Brazil strain, which has been found ineffective against COVID-19.”

These findings mirror findings reported^[2]BCG vaccine protection from severe coronavirus disease 2019 (COVID-19) Luis E. Escobar, Alvaro Molina-Cruz, Carolina Barillas-Mury Proceedings of the National Academy of Sciences Jul 2020, 202008410; DOI: 10.1073/pnas.2008410117 by a group of US researchers in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).

“We found that COVID-19 mortality in the states of New York, Illinois, Louisiana, Alabama, and Florida (unvaccinated) was significantly higher than states from BCG-vaccinated countries (Pernambuco, Rio de Janeiro, and Sao Paulo in Brazil; Mexico State and Mexico City in Mexico).”  wrote co-authors Luis E. Escobar from Virginia Polytechnic Institute and State University, and Alvaro Molina-Cruz and Carolina Barillas-Mury from Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD.  “This is remarkable, considering that three states from Latin America have much higher population densities than the North American states analyzed, including New York”

But the scientists cautioned that correlation does not imply causation.

“The consistent association between BCG vaccination and reduced severity of COVID-19 observed in these and other epidemiological explorations is remarkable, but not sufficient to establish causality between BCG vaccination and protection from severe COVID-19,” they added. “Randomized clinical trials, such as those ongoing in Holland and Australia, in which health workers are administered either the BCG vaccine or a placebo saline injection, will determine the extent to which BCG vaccination in adults confers protection from COVID-19.”